The present invention relates to organic photoconductive compositions for electrophotography that comprise mainly a novel polymer.
A recording method in which a photoconductive substance is used as a photosensitive material is known for the electrophotography. In summary, the method is an image-forming technique that combines electrostatic and photoconductive phenomena of substance. Namely, a highly insulated layer surface is electrostatically charged in the dark, then the charge is dissipated by raising electric conductivity of the exposed part by way of image-wise exposure. This results in the formation of an electrostatic latent image at the non-exposed part, which is then developed, for instance, by contacting it with a colored powder or toner to give a visible image.
Prior art photoconductive layers containing a photosensitive material assembled in electrophotographic copying machines comprise chiefly an organic or inorganic photoconductive material.
Inorganic photoconductive materials are exemplified, for instance, by selenium, zinc oxide, titanium oxide and cadmium sulfide. Although they have a superior photosensitive property, they are inferior having regard to transparency, flexibility, light weight, film-forming property, smooth surface and price. Selenium, in particular, has a disadvantage regarding the toxicity.
On the other hand, organic photoconductive materials are exemplified by condensed polycyclic aromatic compounds such as anthracene, pyrene and perylene, heterocyclic compounds such as pyrazoline derivatives, imidazole derivatives and oxazole derivatives, and polymeric compounds such as poly-N-vinylcarbazole and polyvinylanthracene. They are superior to the above-mentioned inorganic photoconductive materials having regard to transparency, flexibility, light weight, film-forming property, smooth surface and price, hence have extensively been studied for the recent years.
Photosensitive materials containing an organic photoconductive compound, however, have mostly quite a poor photosensitivity as compared with those containing an inorganic photoconductive material such as selenium and zinc oxide, hence only a few of them are practically employed. One of them comprises poly-N-vinylcarbazole (PVK), chemically sensitized with 2,4,7-trinitro-9-fluorenone (TNF). Although it is a photoconductive material having superior properties such as photosensitivity, darkdecay rate, stability and reproducibility, it has a disadvantage owing to the toxicity of TNF.
Further attempts have been made to improve photosensitivity by the combination of an organic photoconductive compound and a dye sensitizer. However, products thus obtained involve practical problems to be overcome such as poor darkdecay rate and reproducibility over a long period of time due to the instability.